Our Research for Shape Memory Alloys (SMA)…

... have been divided into the following parts:

Experimental characterisation of the thermo-/electro-mechanic material properties
Design of actuator/sensor systems
Design of prototypes to highlight effects and uses of the technology
Development of the self-sensing-effects for the manufacture of more compact, sensorless actuator systems
Modelling of SMA-based actuator/sensor systems
Development of advanced control concepts for SMA
Development of the miniaturization and integration of electronics

For a glimpse of our research activities in SMAs please scroll through this page…

What are SMAs?

Shape Memory Alloys, usually made of a Nickel-Titanium alloy, will remain in their shape at low temperatures, and will return to their initial form when heated. The original form allows itself to be diversely adjusted through heating, such that its ducts twist until its original form is reached, in much the same way as contracting wires or springs. The mechanism which allows for the SMA to remember its form is a weight- and temperature-dependent change in its crystal framework that manifests itself between the austenitic and martensitic phases.

FGL-Effekt

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FGL-Effekt

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Actuation and Sensing

For actuation purposes, the device is typically heated via an electric current through the SMA-wire, while the cooling of the wire is passive, done through either convection or conduction. Of all known actuator mechanisms, SMAs have the highest energy densities and are made up of extremely compact, lightweight and silent systems. SMA actuators are mostly in the form of wires or bundles of wires, but springs and rods are also common forms. If you measure the electrical resistance during actuation, one will find it correlates with the contraction of the wire and is able to be utilized as the sensor signal to find the position. Through this the SMA is self-sensing, not requiring external sensors to acquire data. Independent of measuring devices, the cooling rate for the surface area/Volume of the wire (25µm<diameter<500µm) is capable of operating at a resting air density in the range of 30Hz to a very small millihertz value.

Elastocaloric

As a climate-friendly and extremely energy efficient technology to heat and cool, elastocaloric has been demonstrated to be the future alternative to conventional cold compression procedures by the US Department of Energy and the EU Commission. Our lab has, in the six years of research, developed a continuously running technology prototype for the cooling and heating of air and presented it to the Hannovermesse 2019. The technology moves through mechanical load and exoneration of superelastic SMAs and will absorb latent heat, which transforms the kristall structure of the SMA. Air can without climate-harming cooling materials be cooled or heated directly, with the best materials promising an efficiency (COP) of 30.

Elastokalorischer Luftkühler

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Electromechanical Properties and Experiments

For the design of SMA-systems it is imperative to precisely understand the material’s behaviour. For this purpose we have a surplus of modern test devices (most of which having been self-built) readily available, in order to systematically characterise the mechanically coupled demeanour. Tension tests, among others, are measured with the strength and distance as well as the electrical current and voltage, for the purpose of understanding the actuators and sensors. For the characterisation of micro wires with diameters below 20 µm we developed a test device, which will measure Temperatures until 120°C. Furthermore, we have several thermograph cameras equipped with test benches developed in order to understand the elastocaloric behaviours, and to undertake the measurement of the strain-field.

Elastokalorikprüfstand

FGL-Experimente

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Research activities and applications

In addition to the development of new types of elatocaloric cooling aggregates, thermal pumps and thermal power machines, we are also busying ourselves with the development of new actuator concepts. Apart from the utilization of endoscopes in industrial robotics and medicine technic, gripping technologies that are both fast and energy efficient are in focus. Realised through antagonistic concepts, extreme compactness and cost-effective drives can be realised through these materials which, due to their self-sensing properties, would permit a controlled operation without the need for further sensors. Go through the gallery below, in order to see a picture or video of our activities, as well as the potential uses of shape memory alloys.